Rotary drag bits are a type of fixed bladed drill bit that are typically used to shear rock with a continuous scraping motion. A typical fixed bladed bit will comprise a bit body, several blades protruding from the bit body, and a plurality of cutters fixed on the exposed edge of each of the blades. These cutters may be formed from any hard and abrasive material but are generally composed of polycrystalline diamond compact (PDC). A fixed bladed bit may be rotated in an earthen formation allowing the cutters to engage the rock and debris to be removed via the vacant spaces between the blades.
Fixed bladed bits may be designed to optimize cutter efficiency. Methods of designing fixed bladed bits for optimal cutter efficiency may include performing a force balance. A force balance comprises summing the forces on each cutter and calculating the imbalance of forces in relation to the bit. Once a force balance has been performed, modifications may be made to the locations and orientations of the cutters to adjust the forces acting on the bit. This process may be performed several times during the design of a fixed bladed bit.
One such method for designing a rotary drag bit for optimal cutter efficiency is disclosed in U.S. Pat. No. 4,815,342 to Brett, which is herein incorporated by reference for all that it contains. Brett discloses a method for modeling and building drill bits where an array of spatial coordinates representative of selected surface points on a drill bit body and on cutters mounted thereon is created. The array is used to calculate the position of each cutting surface relative to the longitudinal axis of the bit body. A vertical reference plane which contains the longitudinal axis of the bit body is established. Coordinates defining each cutter surface are rotated about the longitudinal axis of the bit body and projected onto the reference plane thereby defining a projected cutting surface profile. In manufacturing a drill bit, a preselected number of cutters are mounted on the bit body. A model of the geometry of the bit body is generated as above described. Thereafter, the imbalance force which would occur in the bit body under defined drilling parameters is calculated, The imbalance force and model are used to calculate the position of an additional cutter or cutters which when mounted on the bit in the calculated position would reduce the imbalance force. A cutter or cutters is then mounted in the position or positions so calculated.
Another such method for designing a rotary drag bit for optimal cutter efficiency is disclosed in U.S. Pat. No. 6,672,406 to Beuershausen, which is herein incorporated by reference for all that it contains. Beuershausen discloses methods including providing and using rotary drill bits incorporating cutting elements having appropriately aggressive and appropriately positioned cutting surfaces so as to enable the cutting elements to engage the particular formation being drilled at an appropriate depth-of-cut at a given weight-on-bit to maximize rate of penetration without generating excessive, unwanted torque on bit. The configuration, surface area, and effective back rake angle of each provided cutting surface, as well as individual cutter back rake angles, may be customized and varied to provide a cutting element having a cutting face aggressiveness profile that varies both longitudinally and radially along the cutting face of the cutting element.